Chemistry deals with the natural world[化学处理的自然世界].ppt

Chapter 16. Section 16-7 Ions as Acids and Bases Chapter 17. Additional Aspects of Acid-Base Equilibria pH of salt solutions Salts: Ionic compounds in which H atoms of acids replaced by metal ions. Hydrolysis: Reaction of a substance with water. Salt hydrolysis: Reaction of an anion or cation, or both ions, of a salt with water. Salts can react with water to be either acidic, basic, or neutral. How can we tell? Salts that yield neutral solutions Salts of strong acids and strong bases e.g. NaOH + HCl ? NaCl + H2O NaCl Na+ + Cl? Na+ + H2O ? no reaction Cl? + H2O ? no reaction a solution of NaCl is neutral. Similarly for NaClO4, LiI, KBr, BaCl2. Salts that yield basic solutions Salts of weak acids and strong bases e.g. CH3COOH + NaOH ? CH3COONa + H2O CH3COONa CH3COO? + Na+ Na+ does not react with water. CH3COO? undergoes hydrolysis: CH3COO? + H2O ? CH3COOH + OH? pH of sodium acetate solution 7 (basic). pH determined by Kb for acetate. Kb = Note: Kb x  Salts that yield acidic solutions Salts of strong acids and weak bases NH4Cl + Cl? NH4+ + H2O ? NH3 + H3O+ Ka = = ? pH of NH4Cl solution 7 (acidic). Salts of weak acids and weak bases Solution pH depends on relative strengths of weak acid and weak base. e.g. NH4NO2 + ? NH3 + H+ Ka = 5.6 x 10?10 + H2O ? HNO2 + OH? Kb = 2.2 x 10?11 Kb Ka ? solution acidic. Salts of weak acids and weak bases acidic if Ka (cation) Kb (anion) neutral if Ka (cation) = Kb (anion) basic if Ka (cation) Kb (anion) Would you expect NH4CN(aq) to be acidic, basic, or neutral? Salts in water can dissociate to be acidic, basic or neutral Examples 1. Is the solution that results when 1 mol of KOH is added to a solution of 1 mol of HNO2 neutral, acidic, or basic? Would aqueous solutions of the following be acidic, basic or neutral? a. KClO